Flexible, stretchable electronic devices

ABSTRACT

Fabrication methods are disclosed that facilitate the production of electronic structures that are both flexible and stretchable to conform to non-planar (e.g. curved) surfaces without suffering functional damage due to excessive strain. Electronic structures including CMOS devices are provided that can be stretched or squeezed within acceptable limits without failing or breaking. The methods disclosed herein further facilitate the production of flexible, stretchable electronic structures having multiple levels of intra-chip connectors. Such connectors are formed through deposition and photolithographic patterning (back end of the line processing) and can be released following transfer of the electronic structures to flexible substrates.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a divisional of U.S. patent application Ser.No. 13/917,302 filed Jun. 13, 2013, entitled “FLEXIBLE, STRETCHABLEELECTRONIC DEVICES.” The complete disclosure of the aforementioned U.S.patent application Ser. No. 13/917,302 is expressly incorporated hereinby reference in its entirety for all purposes.

FIELD

The field of the present disclosure relates to the physical andelectrical sciences, and more particularly to electronic devicesincluding chip connections that facilitate compliance of the electronicelements thereof to surface morphology and methods of manufacturethereof.

BACKGROUND

Flexible electronic systems including flexible integrated circuitdevices are useful for applications wherein such systems must conform tonon-planar surfaces. Conventional electronic components such ascomplementary metal oxide semiconductor (CMOS) circuits are typicallyfabricated on rigid substrates. Various schemes have been employed forrendering rigid/stiff materials flexible by thinning/removing thesubstrate, leaving a relatively thin structure. Such schemes employ, forexample, chemical and mechanical polishing and etching, layer lift-off,controlled spalling, and other methods. Despite the flexibility of thestructures obtained through such schemes, which is due to the relativelysmall total thicknesses thereof, the structures are not stretchable,having limited mechanical properties, i.e. fracture toughness, of theoverall structure in the other two dimensions. A fabrication method forcreating stretchable electronic structures has been proposed thatincludes making small, thin electronic components using lift-offtechniques, transferring small electronic chips to a compliantsubstrate, and subsequently wiring the chips to one another usingserpentine metal wires with low Young's modulus. The relatively smallchip sizes make the wiring task in sophisticated systems complicated andchallenging due to the large number of required electrical connections.

SUMMARY

Aspects of the present disclosure relate to flexible electronicstructures and methods for fabricating such structures.

A first exemplary method includes forming an electronic circuitry layerhaving first and second circuitry regions on a semiconductor substrateand forming a separator layer separating the first and second circuitryregions of the circuitry layer on the substrate. The method furtherincludes forming a layer comprising electrically insulating material onthe circuitry layer, forming an electrical connector layer between thefirst and second circuitry regions and extending across the separatorlayer, and removing the separator layer to form a space beneath theelectrical connector layer, the space further separating the first andsecond circuitry regions of the circuitry layer.

A second exemplary method includes obtaining a structure including i) asemiconductor substrate, ii) a circuitry layer comprising first andsecond circuitry regions deposited on the substrate, the circuitry layercomprising CMOS devices, iii) a separator layer on the substrate thatseparates the first and second circuitry regions of the circuitry layer,iv) a layer comprising electrically insulating material on the circuitrylayer, and v) an electrical connector layer between the first and secondcircuitry regions and extending across the sacrificial separator layer.The exemplary method further includes thinning the substrate, removingthe sacrificial separator layer to form a space above the substrate andbeneath the electrical connector layer, and affixing the substrate to aflexible layer.

An exemplary structure includes a semiconductor substrate including anelectrically insulating layer, a circuitry layer including first andsecond CMOS circuitry regions formed on the substrate and adjoining theelectrically insulating layer, and a first layer comprising electricallyinsulating material on the circuitry layer. A separator layer is on thesubstrate and within the first layer. The separator layer electricallyisolates the first and second CMOS circuitry regions. An electricalconnector layer electrically connects the first and second circuitryregions. The electrical connector layer is formed within the first layerand extends across the separator layer.

As used herein, “facilitating” an action includes performing the action,making the action easier, helping to carry the action out, or causingthe action to be performed. Thus, by way of example and not limitation,instructions executing on one processor might facilitate an actioncarried out by instructions executing on a remote processor, by sendingappropriate data or commands to cause or aid the action to be performed.For the avoidance of doubt, where an actor facilitates an action byother than performing the action, the action is nevertheless performedby some entity or combination of entities.

Substantial beneficial technical effects are provided by the exemplarystructures and methods disclosed herein. For example, one or moreembodiments may provide one or more of the following advantages:

-   -   Enables flexible, stretchable electronic structures;    -   Electrical connections formed by deposition and patterning as        opposed to bonding or soldering;    -   Facilitates providing multiple levels of intra-chip electrical        connections;    -   Monolithic integration of the intrachip connectors facilitates        the integration process.

These and other features and advantages of the present disclosure willbecome apparent from the following detailed description of illustrativeembodiments thereof, which is to be read in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of an exemplary semiconductor oninsulator substrate that may be employed during fabrication of thestructures disclosed herein;

FIG. 2A is a schematic illustration of a structure fabricated inaccordance with a first illustrative embodiment;

FIG. 2B is a schematic illustration of a structure fabricated inaccordance with a second illustrative embodiment;

FIG. 3A is schematic illustration of a structure fabricated inaccordance with a third illustrative embodiment;

FIG. 3B is a top plan view of a portion of the structure shown in FIG.3A;

FIG. 4 is a schematic illustration of a fabrication step includingseparating the structure shown in FIG. 2B from the handle portion of thesubstrate;

FIG. 5A is a schematic illustration of a fabrication step showingremoval of a residual handle layer from the structure shown in FIG. 4;

FIG. 5B is a schematic illustration of a fabrication step showingselective removal of the sacrificial separator layer and residual handlelayer from the structure shown in FIG. 4;

FIG. 5C is a schematic illustration of a fabrication step showingselective removal of the sacrificial separator layer and residual handlelayer from the structure shown in FIG. 4 in accordance with analternative embodiment wherein a low-k dielectric layer encases theelectrical wires connecting at least two circuits;

FIG. 6A is a schematic illustration showing transfer of an exemplarystructure to a flexible substrate and selective removal of thesacrificial separator layer;

FIG. 6B is a schematic illustration showing transfer of a secondexemplary structure to a flexible substrate, and

FIG. 6C is a schematic illustration showing transfer of a thirdexemplary structure to a flexible substrate.

DETAILED DESCRIPTION

Fabrication methods are disclosed that facilitate the production ofelectronic structures that are both flexible and stretchable. Theflexibility of an electronic structure, such as an integrated circuit,allows it to bend to conform to non-planar (e.g. curved) surfaceswithout suffering functional damage due to excessive strain. Anelectronic structure that is also stretchable exhibits tensile strengthand can be stretched or squeezed within acceptable limits withoutfailing or breaking. The methods disclosed herein further facilitate theproduction of flexible, stretchable electronic structures havingmultiple levels of intra-chip connectors. Such connectors are formedthrough deposition and photolithographic patterning (back end of theline processing) in one or more exemplary embodiments and releasedfollowing transfer of the electronic structure to a flexible substrate.

The fabrication methods and electronic structures disclosed herein areamenable to various CMOS manufacturing techniques familiar to those ofskill in the art. It will be appreciated, however, that techniques thatvary in some respects from those disclosed herein may be employed forforming other types of electronic devices that benefit from beingflexible and stretchable. Referring to FIG. 1, a semiconductor oninsulator substrate 20 is obtained. The exemplary substrate includes asilicon handle layer 22, an insulating layer 24 and a semiconductorlayer 26 such as crystalline silicon. The insulating layer 24 in oneexemplary embodiment is a buried oxide layer such as silicon dioxide.The thickness of the semiconductor layer 26 is between 3 nm-30 μm inexemplary embodiments, but thicker or thinner layers may be usable insome applications. Relatively thin semiconductor layers facilitate theproduction of mechanically flexible structures as discussed furtherbelow. The insulator layer 24 in an exemplary embodiment is between10-500 nm, but may be thicker or thinner for some applications. Othersemiconductor substrates such as bulk silicon substrates (not shown) mayalternatively be employed in the fabrication of electronic structures asdisclosed herein.

In one exemplary embodiment, the substrate 20 is employed in thefabrication of an electronic structure as shown in FIG. 2A. An etch stoplayer 32 is formed in the handle layer. Ion implantation is employed toform a heavily doped p+ layer in some embodiments, which functions asthe etch stop layer 32 and further the etch mask protecting the BOXlayer during the removal of the sacrificial separator. The layer isformed as “pockets” in regions beneath the areas that comprise thecircuits (chips). In some embodiments, heavily doped n+ pockets areformed in the handle layer 22 rather than p+ pockets using any suitabletechnique (e.g. ion implantation). Exemplary n-type dopants includearsenic and phosphorus.

An exemplary CMOS process sequence for fabricating a field effecttransistor includes: 1) device isolation (silicon removal to formsilicon “islands” defining the device active region and filling trenchesformed with dielectric material such as silicon dioxide); 2) gate stackand spacer formation; 3) source/drain formation; 4) silicide formationto form contacts to various device electrodes, and 5) middle and backend of the line metallization steps. Referring again to FIG. 2A, acircuitry layer 34 is formed on the crystalline surface layer of thesubstrate 20. The circuitry layer may include any appropriate number,type and configuration of CMOS devices. Exemplary CMOS devices includefield effect transistors, bipolar junction transistors, and non-volatilememory cells, resistors, diodes. Chemical vapor deposition (CVD) isamong the known techniques for depositing materials on crystallinesilicon during CMOS device fabrication. The circuitry layer 34 shown anddescribed hereafter should be considered exemplary as opposed tolimiting. The semiconductor layer 26 between adjoining chips is removed.A contact layer 36 is formed on the circuitry layer 34 for providingelectrical connections between the CMOS devices and other elements.Deposition and patterning techniques familiar to those of skill in theart are employed in one or more exemplary embodiments for forming thecontact layer. Copper and aluminum are among the electrically conductivematerials that can be employed in forming the contact layer 36.Fabrication of the connectors is accordance with one or more embodimentsis conducted during the fifth step of the illustrative sequence.

A separator layer 40 is formed directly on the substrate. While shown onthe insulating layer 24 of the substrate, the separator layer can extendbeyond the insulating layer and inside the silicon handle layer 22. Alayer 38 of electrically insulating material is formed on the substrateover the circuitry layer 34 and contact layer 36. The layer 38 may becomprised of silicon dioxide, silicon nitride or other suitablematerials. In some embodiments, the insulating (BOX) layer 24 and layer38 are comprised of materials that can be selectively etched withrespect to one another. In other embodiments, they are both comprised ofthe same material, silicon dioxide being one exemplary material. Thespacing between chips, which corresponds to the width (L_(space)) of theseparator layer 40, may be based at least in part on the extent to whichthe structure obtained by the fabrication process is intended to stretchor contract. While shown as distinct elements for purpose ofexplanation, the layer 38 of insulating material and the separator layer40 may, at least in part, be comprised of the same material(s) andformed simultaneously. They may alternatively be formed from differentmaterials to facilitate selective etching. As discussed below, theseparator layer 40 is selectively etched with respect to the layer 38and is accordingly shown as a separate element. In some embodiments, theseparator layer includes layers that are not present within the layer 38of insulating material. The layer 38 of insulating material and theseparator layer 40 are formed such that the separator layer ispositioned within the layer 38 of insulating material and between thecircuitry regions 34A, 34B.

Metallization is a further step in back end of the line processing, asknown to those of skill in the art. The metallization step(s) primarilyinvolve deposition, patterning and etching. In an exemplary embodiment,the layer 38 of insulating material is deposited on the substrate, thelayer is patterned using a via mask, and vias are formed in the layerusing an appropriate etching process such as plasma etching. A layer ofmetal such as copper or aluminum is deposited over the entire substrate.Using photolithographic techniques, the metal layer is selectivelyetched. In some embodiments, the metal layers can be formed usingelectrochemical processes such as electroplating. A first metal layer42A is accordingly formed in the chip regions, as shown in the exemplaryembodiment of FIG. 2A. Additional metal layers can be formed as requiredusing the same techniques. In the exemplary embodiment of FIG. 2A, asecond metal layer 42B is formed with associated vias using appropriatedeposition and photolithographic patterning techniques. The second metallayer portions associated with each integrated circuit are electricallyconnected by an electrical connection layer comprising wires 44 that arealso formed during back of the line processing. The wires 44 are alsoformed in the separator layer using deposition, patterning and etchingprocedures and are electrically connected with the second metal layer42B in this exemplary embodiment. It will be appreciated that wirescould additionally be formed within the separator layer 40 to connectthe first metal layer 42A of each chip region, providing multipleintra-chip connection levels. The electrical connections formed by thewires 44 are solderless.

The separator layer is comprised entirely of sacrificial, selectivelyetchable material(s) in some embodiments and comprises a multi-layerstack of different materials in other embodiments. For example, one ormore layers of the separator layer may comprise a low-k dielectricmaterial having a relatively low modulus of elasticity (Young'smodulus). Other layer(s) of the separator layer that are intended to besacrificial may comprise a material having a relatively high Young'smodulus such as silicon dioxide (SiO₂). The low-k dielectric material isformed on a sacrificial layer in the region containing the wires 44. Insuch embodiments, the layer(s) of low-k dielectric material isdeposited, patterned and etched to form vias. Prior to filling the viaswith an electrically conductive material such as copper, a high-kdielectric material is deposited such that the side walls of the viasare coated with the high-k dielectric material. The high-k dielectricmaterial will accordingly coat the metal wires formed during thesubsequent metallization process. Hafnium oxide is an exemplary high-kdielectric material suitable for this process.

FIG. 2B shows an alternative embodiment having a first metal layer 42Aformed within the layer 38 of electrically insulating material and asecond metal layer 42C formed on the structure. The second metal layer42C and associated vias are formed using deposition and patterningtechniques as discussed above on both the layer 38 of insulatingmaterial and the separator layer 40. The portions of the second metallayer 42C formed on the separator layer 40 comprise parts of theconnecting wires 144 between the chip regions. In this exemplaryembodiment, the wires 144 are formed on and within the separator layer40 to resemble a square wave. The wave-like configuration facilitatesstretching and bending of the resulting structure as discussed furtherbelow.

A further alternative embodiment of a structure formed in the mannerdescribed above is illustrated in FIGS. 3A and 3B. The structure issimilar to those shown in FIGS. 2A and 2B and includes the samereference numerals where applicable. In this embodiment, a second metallayer 42D is formed on the structure. The connecting wire 244 betweenthe chip regions is entirely in a plane that is parallel to thecircuitry layer. In other words, no part of the connecting wire extendsnormal to the circuitry layer as in the structures shown in FIGS. 2A and2B. The top plan view of a portion of this structure shows a possibleconfiguration of the connecting wire formed on the separator layer 40.The connecting wires of the disclosed structures are configured to allowrelative movement between circuitry regions without fracturing.

The thickness of the relatively rigid handle layer 22 is reduced once astructure such as shown in FIG. 2A, 2B or 3 is obtained. Varioustechniques may be employed to perform this step. Referring to FIG. 4, astressor layer 50 is adhered to the top surface of the structure of FIG.2B. The stressor layer may be comprised of a metal such as nickel ormultiple layers. A flexible handle layer 52 is operatively associatedwith the stressor layer 50. The flexible handle layer may be comprisedof organic polymeric materials such as polyimide and polyethyleneterephthalate (PET). The stressor and handle layers are employed forcausing a fracture 54 in the rigid handle layer 22 via the controlledspalling. The resulting structure includes a residual silicon layer 56.The handle portion of the initial substrate, once separated from thestructure, can be reused. US 2010/0311250, which is incorporated byreference herein, discloses further exemplary materials and providesadditional information relating to controlled spalling. Controlledspalling techniques could be employed with respect to structures asshown in FIGS. 2A and 3. Other techniques familiar to those of skill inthe art could be employed for thinning the substrate and enhancingflexibility. In some embodiments, chemical/mechanical polishing and/oretching and/or grinding can be used to remove all or part of the rigidhandle layer 22. In other exemplary embodiments, a layer lift-offprocess is used to separate the chips from the handle layer. Such aprocess involves providing an embedded, sacrificial layer (not shown)that is selectively etched.

Removal of the residual layer 56, for example by etching, withoutremoving the separator layer 40 from the structure shown in FIG. 4 layerprovides a structure as shown in FIG. 5A. In the exemplary embodiment ofFIG. 5B, the separator layer 40 is entirely sacrificial and completelyremoved following the removal of the residual layer 56 from thestructure. A space 60 is formed that separates a first region 34A of thecircuitry layer 34 from a second region 34B thereof. The wires 144extend through the space and electrically connect the first and secondregions of the circuitry layer 34. An etching process is employed toremove the sacrificial separator layer. The p+ and/or n+ pockets formedin the handle layer function as an etch mask for the selective removalof the sacrificial separator layer with respect to the insulating (BOX)layer. The portion of the insulating layer 24 beneath the separatorlayer 40 is also removed in the etching process as it does not adjoin anetch stop layer. Reactive ion etching (RIE) and/or wet chemical etchingare among the techniques that may be employed. Etching is conducted fromthe bottom of the structure in the exemplary embodiment of FIG. 5C. Theetchants are chosen based on the material(s) employed for forming theinsulating layers 24, 38 and the separator layer 40 in order to minimizeover-etch of the layers 24 and 38 while removing the separator layer 40.For example, in embodiments where the insulating layer and the separatorlayer are both silicon dioxide, hydrogen fluoride (HF) may beeffectively employed. A combination of dry and wet etches may be used tominimize the over-etch of the insulating layers 24 and 38. The circuitrylayer, metal layer(s) and layer 38 of insulating material should not bematerially affected by the process of removing the separator layer toform the space 60.

Layers of different materials are deposited on the insulating layer 24in some embodiments for forming the separator layer 40. In one exemplaryembodiment, sacrificial material such as silicon dioxide is initiallydeposited on the insulating layer 24. Silicon dioxide has a largeYoung's modulus. A material having a relatively low modulus ofelasticity (Young's modulus), substantially lower than that of silicondioxide, is deposited on the sacrificial portion of the separator layer.This allows the wires (e.g. wires 44, 144) to be formed on and/or withina layer 62 of low-k dielectric material. Examples of low-k dielectricsinclude spin-on organic low-k polymers such as polyimide,polynorborenes, benzocyclobuten, and PTFE. Removal of the residual layer56 and the separator layer 40 from such a structure provides a structureas shown in FIG. 5C wherein the wires are substantially encased by thelayer 62 and thereby protected. As the material comprising the layer 62has a low modulus of elasticity, it can be stretched to an acceptableextent without fracturing, while electrically isolating the wires fromthe adjacent ones. As discussed above, the wire configurations alsofacilitate stretching without fracture and resulting loss of electricalconductivity.

Referring to FIG. 6A, a structure as described above with respect toFIG. 2B is transferred to a flexible substrate 64 in accordance with oneor more embodiments of the fabrication process. The flexible substrate64 includes an adhesive coating (not shown) that will provide adhesionto the structure. Such transfer is effected following removal of thehandle layer 22 and residual layer 56 beneath the insulating layer 24.As discussed above, layer transfer is a technique that can be employedin the fabrication of the structure 70 shown in FIG. 6A. Oncetransferred to the flexible substrate 64, selective removal of thesacrificial separator layer frees the wires 144 connecting the first andsecond circuitry regions 34A, 34B. Etching from the top of the structurein the direction of the insulating layer 24 is conducted in thisexemplary embodiment. The BOX layer 24 may be fully or partially etchedduring the removal of the sacrificial layer. In this exemplaryembodiment, the structure is transferred to the flexible substrate 64having a relatively low Young's modulus prior to removal of theseparator layer. The flexible substrate 64 comprises an elastomericsheet having a low modulus of elasticity, for example about sixtykilopascals to a few megapascals in some embodiments. Exemplarymaterials include polydimethylsiloxane (PDMS) and polyvinyl alcohol(PVA). Young's modulus for PDMS has been found to be in the range of360-870 KPa. In one or more embodiments, the thickness of the flexiblesubstrate is between twenty and two hundred microns.

In an alternative embodiment as shown in FIG. 6B, a structure istransferred to a flexible substrate followed by the removal of anybacking layer (not shown) that may be employed in a lift-off process ora stressor layer 50 if a controlled spalling process has been previouslyperformed. In this embodiment, the separator layer 40, which is entirelysacrificial, is removed prior to transferring the structure to theflexible substrate 64. In one exemplary embodiment, a structure as shownin FIG. 5B is first obtained. This structure is then transferred to theflexible substrate 64 and the stressor layer 50 is removed to obtain thestructure 75 shown in FIG. 6B. If the stressor layer is metal, aninsulating layer is deposited to separate the metal stressor layer fromthe contacts. The stressor layer may be removed via chemical etch. Theetch stop regions 32 shown in FIG. 6B could alternatively comprise aresidual silicon layer 56. The etch stop regions are optional in someembodiments.

In another exemplary embodiment, a structure as shown in FIG. 5C isobtained. The structure is transferred to a flexible substrate 64followed by removal of the stressor layer 50 and flexible handle layerto provide the structure 80 shown in FIG. 6C.

Given the discussion thus far, an exemplary structure has asemiconductor substrate including an electrically insulating layer 24and a circuitry layer comprising first and second CMOS circuitry regions34A, 34B formed on the substrate and adjoining the electricallyinsulating layer. A first layer 38 comprising electrically insulatingmaterial adjoins the circuitry layer. A separator layer 40 within thefirst layer electrically isolates the first and second CMOS circuitryregions. An electrical connector layer electrically connects the firstand second circuitry regions. The electrical connector layer is formedwithin the first layer and extends across the separator layer. A furtherexemplary structure is obtained by removing the separator layer, leavingthe electrical connector layer in place. As shown, for example, in FIGS.6A-C, the circuitry regions 34A, 34B remain connected by one or moreserpentine connector wires 144 that allow the structures 70, 75, 80 tobe stretched or squeezed without damage. As the wires 144 are formedduring back end of the line processing, the difficulties associated withwiring circuitry regions following the CMOS fabrication process usingsoldering or other techniques is avoided.

A first exemplary method includes forming an electronic circuitry layer34 having first and second circuitry regions 34A, 34B on a semiconductorsubstrate 20. A separator layer 40 is formed on the substrate thatseparates the first and second circuitry regions. A layer 38 comprisingelectrically insulating material is formed on the circuitry layer. Anelectrical connector layer, including for example wires 44, 144 or 244,is formed between the first and second circuitry regions and extendsacross the separator layer. The separator layer 40 is removed to form aspace 60 beneath the electrical connector layer. The space 60 separatesthe first and second circuitry regions of the circuitry layer 34. Insome embodiments, the wires are suspended in air following formation ofthe space 60. In other embodiments, the wires are embedded in a materialhaving a low Young's modulus.

A second exemplary method includes obtaining a structure including asemiconductor substrate 20, a circuitry layer 34 comprising first andsecond circuitry regions 34A, 34B deposited on the substrate, thecircuitry layer comprising CMOS devices, a separator layer 40 on thesubstrate that separates the first and second circuitry regions of thecircuitry layer, a layer comprising electrically insulating material onthe circuitry layer, one or more metal layers within the electricallyinsulating material, and an electrical connector layer 44, 144, 244between the first and second circuitry regions and extending across thesacrificial separator layer. The exemplary method further includesthinning the substrate, removing at least part of the separator layer toform a space 60 beneath the electrical connector layer and within thelayer comprising electrically insulating material, and affixing thesubstrate to a flexible layer. In one or more embodiments, the step ofremoving at least part of the separator layer 40 is performed subsequentto affixing the substrate to the flexible layer.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the invention. Asused herein, the singular forms “a”, “an” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises”and/or “comprising,” when used in this specification, specify thepresence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof. Terms such as “top” and “bottom” areused to designate relative positions of elements as opposed toelevation. For example, the “top” surface of a structure can face up,down, or any other direction.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to the invention in the form disclosed. Many modifications andvariations will be apparent to those of ordinary skill in the artwithout departing from the scope and spirit of the invention. Theembodiment was chosen and described in order to best explain theprinciples of the invention and the practical application, and to enableothers of ordinary skill in the art to understand the invention forvarious embodiments with various modifications as are suited to theparticular use contemplated.

What is claimed is:
 1. A structure comprising: a semiconductor substrateincluding an electrically insulating layer; a circuitry layer comprisingfirst and second CMOS circuitry regions formed on the substrate andadjoining the electrically insulating layer; a first layer comprisingelectrically insulating material on the circuitry layer; a separatorlayer on the substrate and within the first layer, the separator layerelectrically isolating the first and second CMOS circuitry regions; anelectrical connector layer electrically connecting the first and secondcircuitry regions, the electrical connector layer being formed withinthe first layer and extending across the separator layer.
 2. Thestructure of claim 1, wherein the separator layer comprises asacrificial layer adjoining the substrate and a second layer on thesacrificial layer, the second layer having a substantially lower Young'smodulus than the sacrificial layer, the electrical connector layeradjoining the second layer.
 3. The structure of claim 1, furtherincluding a first and second etch stop regions within the substrate, thefirst CMOS circuitry region being positioned over the first etch stopregion and the second CMOS circuitry region being positioned over thesecond etch stop region, the separator layer being positioned over aportion of the substrate between the first and second etch stop regions.